Durability of District Heating Pipelines Exposed to Thermal Aging and Cyclic Operational Loads

Fourth generation district heating networks (4GDH) must be designed for future energy systems, integrating renewable volatile energy sources, with lower operation temperatures, and consequent reduction of heat losses and increased energy efficiency. The lower levels of operating temperature and the greater amount of cyclic loading, influence aging, and the service life of 4GDH pipelines, differently from traditional district heating (DH) networks, and thus require proper investigation of the system response at the cross-sectional level. To evaluate the material durability of 4GDH pipelines, we have analyzed the behavior of the service steel pipe, the insulation foam, and their adhesive interaction, using an innovative analytical and experimental procedure. This paper describes the influence of traditional and future operational loading conditions on the performance of preinsulated bonded single-pipe systems, representing the majority of currently operating DH pipelines. The performed fatigue analysis of the steel service pipe showed that the lifetime of 4GDH pipelines is expected to increase because of the lower operating temperature, and the low impact of thermal loading volatility in the network, compared to conventional DH. The accelerated aging tests of DN